The principal objective of the research proposed herein is the development of a new and general synthetic protocol for the prepatation of a variety of medicinally important alkaloids. The target structure, a pyrrolidine or 3-pyrroline fused to another ring with the nitrogen at the bridgehead position, is widely spread in nature. To prepare this subunit, intramolecular l,3-dipolar cycloaddition of an axide onto a diene is proposed. The resultant vinyl triazoline will then be transformed into a 3-pyrroline by photolysis. The ease of preparation of the azido diene precursors as well as the opportunity for rapid construction of alkaloidal ring systems with appropriate stereocenter incorporation makes this work potentially very significant. The flexibility of this method will be demonstrated by the synthesis of a number of biomedically significant compounds (pyrrolizidine alkaloids, swainsonine, slaframine, pumiliotoxins, gephyrotxin). Within the framework of these syntheses, several unexplored areas in the chemistry of vinyl triazolines and vinyl aziridines will be addressed. As a concurrent goal, a new method for the synthesis of optically pure heteroacids is proposed, which will be utilized as chiral starting materials for the above alkaloid syntheses. The fusion of certain heterocycles (l,3-dioxolan-4-ones, 4H-1,3-dioxin-4-ones, for example) to chiral auxilliaries will provide rigid frameworks for the transfer of stereochemical information during carbon-carbon bond forming reactions. In this way, Alpha- and Beta-hydroxyacids of amino acids and their derivatives will be prepared.